drm/vc4: Limit fkms to modes <= 85Hz

Selecting 1080p100 and 120 has very limited gain, but don't want
to block VGA85 and similar.

Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.org>

drivers/gpu/drm/vc4/vc4_firmware_kms.c

@@ -822,6 +822,10 @@ vc4_crtc_mode_valid(struct drm_crtc *crtc, const struct drm_display_mode *mode)
 		return MODE_NO_DBLESCAN;
 	}
 
+	/* Disable refresh rates > 85Hz as limited gain from them */
+	if (drm_mode_vrefresh(mode) > 85)
+		return MODE_BAD_VVALUE;
+
 	/* Limit the pixel clock based on the HDMI clock limits from the
 	 * firmware
 	 */